Flag枚举中所有值的表示

Question

我希望在我的python Flags枚举中有一个"ALL"标志

myenum.EVERY_MEMBER & myenum.ALL == myenum.EVERY_MEMBER

是的.我目前有:

from enum import Flag, auto

class RefreshFlags(Flag):
    NONE = 0
    EVENTS = auto()
    RESOURCES = auto()
    BUILDINGS = auto()
    DEFENSES = auto()
    .....

因为这个枚举可能会在任何开发状态下增长,我希望有类似的东西

@property
def ALL(self):
    retval = self.NONE
    for member in self.__members__.values():
        retval |= member
    return retval

这不起作用:

RefreshFlags.EVENTS  & RefreshFlags.ALL

TypeError: unsupported operand type(s) for &: 'RefreshFlags' and 'property'

请注意,此问题目前仅与python 3.6或更高版本有关.

Answer 1

有几种方法可以解决这个问题:

• 用一个classproperty(见 Zero's answer)

• 使用类装饰器(参见参考资料MSeifert's answer)

• 使用mixin(currently buggy)

• 创建一个新的基类(见下文)

使用类属性方法需要注意的一件事是,由于描述符是在类而不是元类上定义的,因此缺少对设置和删除的常规保护 - 换句话说:

>>> RefreshFlags.ALL
<RefreshFlags.DEFENSES|BUILDINGS|RESOURCES|EVENTS: 15>

>>> RefreshFlags.ALL = 'oops'
>>> RefreshFlags.ALL
'oops'

创建一个新的基类:

# lightly tested
from enum import Flag, auto
from operator import or_ as _or_
from functools import reduce

class AllFlag(Flag):

    @classproperty
    def ALL(cls):
        cls_name = cls.__name__
        if not len(cls):
            raise AttributeError('empty %s does not have an ALL value' % cls_name)
        value = cls(reduce(_or_, cls))
        cls._member_map_['ALL'] = value
        return value

在使用中:

class RefreshFlag(AllFlag):
    EVENTS = auto()
    RESOURCES = auto()
    BUILDINGS = auto()
    DEFENSES = auto()

>>> RefreshFlag.ALL
<RefreshFlag.DEFENSES|BUILDINGS|RESOURCES|EVENTS: 15>

该ALL属性的有趣区别在于名称的设置_member_map_- 这允许为Enum成员提供相同的保护:

>>> RefreshFlag.ALL = 9
Traceback (most recent call last):
  ....
AttributeError: Cannot reassign members.

但是,这里存在竞争条件:如果在第一次激活之前RefreshFlag.ALL = ...发生, RefreshFlag.ALL那么它就会被破坏; 出于这个原因,我会在这个实例中使用装饰器,因为装饰器会在它被破坏之前处理Enum.

# lightly tested

from enum import Flag, auto
from operator import or_ as _or_
from functools import reduce

def with_limits(enumeration):
    "add NONE and ALL psuedo-members to enumeration"
    none_mbr = enumeration(0)
    all_mbr = enumeration(reduce(_or_, enumeration))
    enumeration._member_map_['NONE'] = none_mbr
    enumeration._member_map_['ALL'] = all_mbr
    return enumeration

在使用中:

@with_limits
class RefreshFlag(Flag):
    EVENTS = auto()
    RESOURCES = auto()
    BUILDINGS = auto()
    DEFENSES = auto()

>>> RefreshFlag.ALL = 99
Traceback (most recent call last):
  ...
AttributeError: Cannot reassign members.

>>> RefreshFlag.ALL 
<RefreshFlag.DEFENSES|BUILDINGS|RESOURCES|EVENTS: 15>

>>> RefreshFlag.NONE
<RefreshFlag.0: 0>

Answer 2

TL;DR 因为属性仅在类的实例上评估，而__members__只能在类上访问。

如果您访问一个property类，它只会返回一个property：

>>> RefreshFlags.ALL
<property at 0x2a5d93382c8>

但是，要使其工作，您需要将其设为类方法：

from enum import Flag, auto

class RefreshFlags(Flag):
    NONE = 0
    EVENTS = auto()
    RESOURCES = auto()
    BUILDINGS = auto()
    DEFENSES = auto()

    @classmethod
    def ALL(cls):
        retval = self.NONE
        for member in cls.__members__.values():
            retval |= member
        return retval

>>> RefreshFlags.ALL()
<RefreshFlags.DEFENSES|BUILDINGS|RESOURCES|EVENTS: 15>

或访问实例上的属性：

from enum import Flag, auto

class RefreshFlags(Flag):
    NONE = 0
    EVENTS = auto()
    RESOURCES = auto()
    BUILDINGS = auto()
    DEFENSES = auto()

    @property
    def ALL(self):
        retval = self.NONE
        # One needs to access .__class__ here!
        for member in self.__class__.__members__.values():
            retval |= member
        return retval

>>> RefreshFlags.EVENTS.ALL
<RefreshFlags.DEFENSES|BUILDINGS|RESOURCES|EVENTS: 15>

在这两种情况下，您都可以稍后进行比较：

>>> RefreshFlags.EVENTS & RefreshFlags.EVENTS.ALL
<RefreshFlags.EVENTS: 1>

您在评论中表示您希望该ALL成员表现得像其他人一样，在这种情况下，我建议使用类装饰器：

def with_ALL_member(enumeration):
    retval = enumeration(0)  # in case NONE is not defined
    for name, member in enumeration.__members__.items():
        retval |= member
    enumeration.ALL = retval
    return enumeration

@with_ALL_member
class RefreshFlags(Flag):
    NONE = 0
    EVENTS = auto()
    RESOURCES = auto()
    BUILDINGS = auto()
    DEFENSES = auto()

>>> RefreshFlags.EVENTS & RefreshFlags.ALL
<RefreshFlags.EVENTS: 1>

>>> RefreshFlags.DEFENSES & RefreshFlags.ALL
<RefreshFlags.DEFENSES: 8>

类装饰器也可以用于其他枚举:)

Answer 3

根据 MSeifert 的回答，可以编写一个@classproperty装饰器，它允许您直接作为属性进行访问RefreshFlags.ALL（而不是作为常规方法或实例上的属性）：

from enum import Flag, auto
from operator import or_
from functools import reduce


class classproperty:

    def __init__(self, func):
        self._func = func

    def __get__(self, obj, owner):
        return self._func(owner)


class RefreshFlags(Flag):

    NONE = 0
    EVENTS = auto()
    RESOURCES = auto()
    BUILDINGS = auto()
    DEFENSES = auto()

    @classproperty
    def ALL(cls):
        return reduce(or_, cls)

您当然可以像示例中那样ALL()使用显式循环编写；for以上仅作为替代方案提供。

>>> RefreshFlags.ALL
<RefreshFlags.DEFENSES|BUILDINGS|RESOURCES|EVENTS: 15>
>>> RefreshFlags.ALL & RefreshFlags.BUILDINGS
<RefreshFlags.BUILDINGS: 4>